Process of case hardening



ha s M22, 1931 UNITED STATES PATENT orrlcs sons .1. near, or new rear. America we mare mmuaorcar. comm, a conrona'rzon or war vmema m CA8] KAI-DII'IIG Io Drawing.

My invention relates to the production of nitrided layers on metals by heating the metals in nitro n-containing agents, such as am monia. It as particular reference to an'im- 5 proved method of forming such hard wearrcsistant cases.

The object 'of my invention is to rovide means for accelerating and intensifym the action of nitriding gases on metal artic es so as to reduce the time required to produce a case of given hardness or thickness.

The case harde of alloys is useful as a means of formin ard wearing surfaces on articles to be use for various machine and tool parts. In order to avoid the formation of brittle cases or cause any other deleterious efl'ect upon the material being treated the nitriding process is referably carried out at low tem ratures. 0 permit the production m of a satisfactolg case at temperatures of the order of 460 to 580 C. it is often customary to alloy with the material to be treated small amounts of a promoting agent such as aluminum or vanadium. A heating period of from 12 to hours in a nitriding atmosphere such as ammonia is usually required to cm a suitable case, the lengt of time of treatment increasin with a decrease in temrature. Such pro onged heating which has n necessary to insure a proper reaction is xpensive. I

have found that hard nitrogen-containing cases ma be produced in much less time by the emp oyment of influences acting to ionize the nitnding agent. Such ionizing infinance may be generated by an arc, spark,

corona or other vform ofivelectrical dlschlllife in the nitriding gas in a manner gener y similar to the way in which ionizing in fluences have heretofore been used in chemical synthesis.

In accordance with my invention the specimen to be treated is placed in a suitable chamber containing anvatmosphere of ammonia or other nitriding gas, and an electrical.dis-- charge is caused to take place within the chamber, referably in close proximity to the surface of the specimen. The usual nitriding 0 temperature is maintained and the discharge is continued throughout the entire time of Application fled Kay as, 1980. Serial Io.

heating. Suitable electrodes across which an arc inay be drawn can be easily inserted into the nitriding chamber. A spark such as may be obtained from the ordinary spark pl is an especiall convenient form 0 electri discharge for is purpose. With one or more spark plugs dischargm the nitriding atm here I have Eeen able to, produce a case in our hours which is ual in hardness and depth to' one produced y the usual nitriding grocess on a similar metal article in twenty ours.

The speed of the nitriding reaction a pears to increase the closer the location of t e discharge to the surface of the specimen bemg treated. I therefore prefer a method in which the cimen itself acts as an electrode and a smal are or s ark is drawn from the surface of the me to one or more other electrodes inserted into the nitriding chamber. By this latter method only two hours treatment is required to produce a hardened layer the, equivalent of one formed in thirty or more hours under the same conditions without any ionizing influence. 75

While cannot explain precisely the mechan sm of the reaction, it ap that the mmzm influence ctmverts e nitridmg gas, suc as ammonia, into a more active form which accelerates the nitriding reaction. By drawing an are from the itself the dissociation takes place very near to or directlyon the surface of the metal at a point where the active gas may more read- 11y enter into the nitridi reaction bforet has time to recombine. is may account In part for the t acceleration obtained by the latter method. I

Since other factors may also contribute to produce the results herein shown, the invention should not be restricted by an attempt to describe the theory involved. While the preferred form of ionizing influence consists of an electrical discharge within the nitriding chamber, it will be evident that other means of causing ionization may also be used without departing from the spirit of my .mvention as defined in the appended claims.

I claim:

1. The method of nitriding metal articles which com rises heating the articles in the presence 0 a nitriding agent and subjecting said nitriding agent to an ionizing electrical discharge.

2. The method of nitriding metal articles which comprises heating the articles in a chamber containing a nitriding atmosphere and introducing within said chamber an electrical discharge for ionizing said nitriding atmosphere. 3

3. The method of nitriding metal articles which comprises heating the articles in a chamber containing an atmosphere of ammonia and causing an electrical discharge to take place within said chamber.

4. The method of nitriding metal articles which comprises heating the articles in a chamber containing an atmosphere of ammonia and causing a spark discharge to take place within said chamber in close proximity to the surface of said articles.

5. The method of nitriding metal articles which comprises heating the articles in a chamber containing an atmosphere of ammonia, inserting electrodes within said chamber, and causing a spark discharge between said electrodes while the articles are being heated, said spark being in close proximity to the surface of said articles.

6. The method of nitriding metal articles which comprises heating the articles in a chamber containing an atmosphere of ammonia, inserting electrodes within said chamber, and drawing a spark between said electrodes and the surface of said articles while they are being heated.

In testimony whereof, I aflix my si nature.

JOHN J. E AN.

which com rises heating the articles in the presence 0 a nitriding agent and subjecting said nitriding agent to an ionizing electrica discharge.

2. The method of nitriding metal articles which comprises heating the articles in a chamber containing a nitriding atmosphere and introducing within said chamber an electrical discharge for ionizing said nitriding atmosphere.

3. The method of nitriding metal articles which comprises heating the articles in a chamber containing an atmosphere of ammonia and causing an electrical discharge to take place within said chamber.

4. The method of nitriding metal articles which comprises heating the articles in a chamber containing an atmosphere of ammonia and causing a spark discharge to take place within said chamber in close proximity to the surface of said articles.

5. The method of nitriding metal articles which comprises heating the articles in a chamber containing an atmosphere of ammonia, inserting electrodes within said chamber, and causing a spark discharge between said electrodes while the. articles are being heated, said spark being in close proximity to the surface of said articles.

6. The method of nitriding metal articles which comprises heating the articles in a chamber containing an atmosphere of ammonia, inserting electrodes within said chamber, and drawing a spark between said electrodes and the surface of said articles while they are being heated.

In testimony whereof, I aflix my si nature.

JOHN J. E AN.

CERTIFICATE OF CORRECTION.

Patent No. 1,837,256. Granted December 22. 1 3 to JOHN J. EGAN.

It is hereby certified that the name of the assignee in the above numbered patent was erroneously described and specified as "Electric Metallurgical Company", whereas said name should have been described and specified as Electro Metallurgical Company, as shown by the records of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of February, A. D. 1932.

M. J. Moore,

(Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 1,837,256. Granted December 22. l93l. to

JOHN J. EGAN.

It is hereby certified that the name of the assignce in the above numbered patent was erroneously described and specified as "Electric Metallurgical Company", whereas said name should have been described and specified as Electro Metallurgical Company, as shown by the records of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of February, A. D. 1932.

. n, M. J. Moore, (Seal) Acting Commissioner of Patents. 

